Many factories operate on the "just-in-time" principle which means that component parts are delivered to an assembly area only when they are needed. Normally there will be minimal staging of parts waiting to be used. This principle is efficient in its use of factory space but it can cause substantial problems if there is any breakdown in the supply pipeline.
The "just-in-time" principle depends on a proper staging of parts from the manufacturer to the assembly area, whether the manufacturer be an outside supplier or just another area of the factory. In some instances it is desirable to have a small supply of parts waiting for transfer to a "pick" area, being an area where one or more operators will attend to pick up parts to be used in an assembly operation. In order to maintain a proper flow it is essential that a new supply of parts be transferred to the pick area as soon as the old supply of parts is depleted.
Parts for assembly operations are usually provided on pallets or in large bins. If the parts are heavy the pallets or bins must be moved by fork lift trucks or other similar powered pallet or bin movers. This can pose a timing or scheduling problem; also there must be someone on call to drive a fork lift truck to transfer a new pallet or bin to the pick area.
It would be desirable to be able to provide a first supply of parts to a pick area with a second supply waiting, or "staged" so that with a push of a button the second supply could be automatically brought to the pick area. A new supply could then be brought to the staging area at any time during the period in which parts are being taken from the second supply. Safety and scheduling aspects of the operation would be improved and there would be more flexibility in the usage of available manpower.